Crossed molecular beam: I. Photoionization studies of hydrogen sulfide and its dimer and trimer, II. A rotating source crossed molecular beam apparatus

摘要

Photoionization efficiency data for H(,2)S(\u27+), S(\u27+) and HS(\u27+) have been obtained in the region 645-1190 (ANGSTROM) using the molecular beam method. The ionization energy of H(,2)S was determined to be 10.4607 (+OR-) 0.0026 eV (1185.25 (+OR-) 0.30 (ANGSTROM)). The observed autoionizing vibrational progressions are tentatively assigned to the Rydberg transitions: 5a(,1) (---\u3e) nsa(,1) (n = 5 and 6) and 2b(,2) (---\u3e) nda(,1) (n = 4 and 5). The internal energy effects and the energetics of the ion-molecule reactions H(,2)S(\u27+) + H(,2)S (---\u3e) S(,2)(\u27+) + 2H(,2), HS(,2)(\u27+) + H(,2) + H, H(,3)S(\u27+) + HS, and H(,3)S(,2)(\u27+) + H have been studied by photoionization of hydrogen sulfide dimers which were synthesized by the molecular beam method. The appearance energy (AE) for H(,3)S(\u27+) from (H(,2)S)(,2) was determined to be 10.249 (+OR-) 0.012 eV (1209.7 (+OR-) 1.5 (ANGSTROM)). This value allows the calculation of the absolute proton affinity for H(,2)S at 0 K to be 167.2 (+OR-) 1.4 kcal/mol. Using the measured ionization energies for (H(,2)S)(,2)(\u27+) (9.596 (+OR-) 0.022 eV) and (H(,2)S)(,3)(\u27+) (0.467 (+OR-) 0.022 eV) and the estimated bonding energies for H(,2)S(.)H(,2)S and (H(,2)S)(,2)(.)H(,2)S(0.05 eV), the bond dissociation energies for H(,2)S(\u27+)(.)H(,2)S and (H(,2)S)(,2)(\u27+)(.)H(,2)S are deduced to be 0.92 (+OR-) 0.04 and 0.18 (+OR-) 0.04 eV, respectively. The AE for H(,3)S(\u27+)(.)H(,2)S from (H(,2)S)(,3) (9.84 (+OR-) 0.04 eV) also makes possible the calculation of the bond dissociation energy for H(,3) H(,3)S(\u27+)(.)H(,2)S to be 0.46 (+OR-) 0.10 eV;In the second part, a unique experimental apparatus is described for crossed neutral-neutral molecular beam studies; a rotating source crossed molecular beam apparatus. Each of the two independently rotatable beam sources is provided with two stages of differential pumping. The present beam source chambers permit any molecular beam crossing angle between 180 and 60 degrees. The detector chamber has three differentially pumped regions, the innermost of which contains the electron bombardment ionizer, quadrupole mass filter, and ion counting system which constitute the detector. This stationary detector chamber permits strong differential pumping in all regions and allows the entire detector to be translated, in vacuo over a distance of (TURN)60 cm beginning (TURN)27 cm from the beam crossing region. A particularly attractive feature of;this flexible design is the expected ease with which techniques utilizing lasers may be incorporated; (\u271)USDOE Report IS-T-1113. This work was performed under Contract W-7405-Eng-82 with the U.S. Department of Energy.